It is well known that waste gases such as highly toxic, pyrophoric and flammable waste gases can be safely disposed of by burning the gases in a controlled combustion incinerator. A combustion incinerator for burning such gases is available commercially under the trademark GUARDIAN, which trademark is owned by Hoechst A. G. During the combustion of waste gases, combustion products are formed that could adhere to the walls of the combustion chamber. Generally, the combustion chamber is equipped with a thermocouple and at least one ignitor port. Heavy deposits of combustion products on the thermocouple could result in insulating the thermocouple from the heat of the reaction chamber and possibly cause a spurious low temperature reading. This false reading could activate a safety alarm and result in a needless maintenance check on the system. The buildup of combustion products on the ignitor ports could result in a restriction of the flow of the combustion fuel into the chamber to maintain a safe operating temperature in the reaction zone. It is also possible that the fuel supply from the ignitor port could be completely blocked and thus cause an actual stoppage of the combustion in the chamber. Without a permanent flame and flow of fuel in the combustion chamber, flammables and pyrophorics may not be completely converted to nonflammable materials. It is well known that when the waste gas is silane, dilution of the silane will not necessarily prevent silane fires and explosions.
A solution to the problem of combustion product buildup is to use pulsed blasts of high pressure clean dry air against the side wall of the combustion chamber and the face of the thermocouple. When the waste gas is silane-based gases or dichlorosilane gases, the combustion incinerator burns large quantities of these waste gases, frequently at high gas flow rates such as from 3 to 6 standard cubic feet per minute. Most of the solid combustion product (almost entirely silicon dioxide or silica) is entrained with the large air flow through the incinerator and is carried downstream where it is collected. However, during high flowrate burns, solid combustion product builds up rapidly on the wall of the combustion's reaction chamber. Under these conditions, experience showed that the pulse blast air system did not clean the reaction chamber nearly well enough to permit safe, unattended operation of the incinerator.
A conventional incinerator has a duct of circular cross section through which combustion air is drawn by the fan of a downstream scrubber or baghouse (filter). The integral reaction chamber, also with a circular cross section is centered closest to the air-inlet end of the duct and perpendicular to the axis of the duct. Waste gases are introduced into the incinerator by a number of high pressure and/or low pressure pipes attached to the chamber. At two locations 90 degrees apart, there are ignitors inserted into ports in the reaction chamber wall. A fuel, preferably hydrogen and clean dry air (CDA) are supplied to each ignitor and are mixed therein. Each ignitor is fitted with a continuously firing spark plug which ignites the fuel-air mixture creating a horizontal flame front in the reaction chamber. Incoming waste gases pass through the flame front where they are ignited and burn in a shearing flow created at the lower end of the reaction chamber where the downwardly flowing gases meet with a perpendicular air flow. The air drawn into the duct is much in excess of that needed for stoichiometric combustion of the waste gases. The excess air cools the combustion products before they leave the exhaust end of the duct. Air drawn into the duct is set to have a flow velocity at least three times greater than the flame velocity of hydrogen which is the fastest burning gas. This is intended to prevent flame exit from the air-inlet end of the duct.
An electronic controller could be used to monitor a number of the operational variables of the incinerator, such as fuel pressure, temperatures, air flow velocity, ignitor power, and line voltage. The controller provides audible and visual warnings. It also provides control signals for interconnection with other waste product disposal system equipment. The reaction chamber and exhaust gas temperatures could be monitored by the controller by means of a thermocouple inserted into the reaction chamber and into the exhaust end of the incinerator's duct. There are preset limits, upper and lower, on the reaction chamber temperature, and there are upper limits imposed on the exhaust gas temperature because of other process equipment downstream. For safe operation of the incinerator, the reaction chamber temperature is normally between 350.degree. C. and 1150.degree. C. Exhaust gas temperature is usually limited to 200.degree. C. but may be as high as 400.degree. C. depending on the downstream equipment and the flowrate at which waste gases are burned in the reaction chamber.
As stated above, it was found that occasionally the pulsed blast of high pressure clean dry air did not clean the reaction chamber satisfactorily during periods of high waste gas burn rates of 3 to 6 standard cubic feet per minute. This resulted in too much buildup of combustion products remaining on the thermocouple, reaction chamber walls, and on the ignitor ports even after the pulsed blast of high pressure clean dry air was used.
It is an object of the present invention to provide a mechanical wiper means for effectively and efficiently removing combustion product buildup from the inner wall of a waste gas incinerator.
It is another object of the present invention to provide a mechanical wiper means for removing combustion product buildup from the ignitor ports and a thermocouple projected from the inner wall of a waste gas incinerator.
It is another object of the present invention to provide a cost effective means for removing combustion product buildup on the wall of a waste gas incinerator.